1. Field of the Invention
This invention relates to a conveying system provided in a device of manufacturing electronic substrates such as semiconductor wafers, liquid crystal substrates and semiconductor disk to convey workpieces such as semiconductor wafers set in a container.
2. Background
For instance, semiconductor devices are manufactured in a clean room in which the atmosphere has been cleaned. As for a conveying system of conveying semiconductor wafers (hereinafter referred to merely as "wafers", when applicable) between processing stations in the clean room or stores them in a stocker, a technique is known in the art that, in order to prevent the wafers from being contaminated by dust, a wafer cassette containing the wafers is hermetically set in a portable container, and the wafer cassette thus set is conveyed or stored.
FIG. 4 is a perspective view of a semiconductor stocker 1 of this type, and FIG. 5 is a front view showing the inside of the semiconductor stocker 1. The stocker 1 has a cassette entrance 1A and a container entrance 1B (shown only in FIG. 4). The stocker 1 has a workpiece transferring chamber 1C on the side of the cassette entrance 1A, and a container storing chamber 1D on the side of the container entrance 1B. FIG. 6a is a diagram showing a cassette 2, FIG. 6b is a diagram showing a container body 3A, and FIG. 6c is a diagram showing a bottom lid 4 engaged with the container body 3A. A container 3 is formed by combining the bottom lid 4 with the container body 3A.
The cassette 2 is in the form of a box with one end opened. A plurality of wafers W (usually twenty-five (25) wafers) are stacked in the cassette 2 in such a manner that they are spaced from one another. The container body 3A is in the form of a box with no bottom. A pair of handles 3B and 3B are secured to right and left side walls of the container body 3A, and a handle 3C is secured to the top wall of the container body 3A. The handles 3B are to be held by a robot 10 (described later), and the handle 3A is to be held by an operator. The bottom lid 4 is engaged with the bottom of the container body 3A. More specifically, the bottom lid 4 is detachably engaged with the container body 3A as follows: The bottom lid 4 has lock arms (not shown) inside it, and holes 4A in the side surfaces through which the end portions of the lock arms are extended outside. The end portions of the lock arms extended through the holes 4A are inserted into recesses (not shown) formed in the inner surfaces of the side walls of the container body 3A. Thus, the bottom lid 4 is detachably engaged with the container body 3A. The arrangements of those structures will be described with reference to an embodiment of the invention in detail.
The cassette 2 is accommodated in the container 3 as follows: First, the cassette 2 is positioned on the bottom lid 4 as required. For this purpose, a positioning piece (not shown) is provided on the upper surface of the bottom lid 4, and a guide (not shown) is provided on the bottom of the cassette 2. The guide of the cassette 2 is engaged with the positioning piece of the bottom lid 4 so that the cassette 2 is correctly positioned on the bottom lid 4. Under this condition, the cassette 2 is covered with the container body 3A from above, and then the end portions of the lock arms are protruded through the holes 4A from the bottom lid 4, so that the latter 4 is fixedly secured to the container body 3A to form the container 3. The container 3 thus formed is moved into the container storing chamber 1D. As the case may be, the container 3 is taken out of the container storing chamber 1D and moved out of the stocker 1 through the container entrance 1B. The above-described operations are carried out by a robot 10 provided inside the stocker 1.
In FIG. 5, reference numeral 11 designates a Y-axis guide rail for the vertical movement of the robot 10. The Y-axis guide rail 11 is supported by a slider (not shown) in such a manner that it together with the slider is movable in a direction (Z-axis) perpendicular to the surface of the drawing. A first slider 12 is supported by the Y-axis guide rail 11 in such a manner that it is vertically movable. An X-axis guide rail 13 is secured to the Y-axis guide rail 11. A second slider 14 is supported by the X-axis guide rail 13 in such a manner that it is movable longitudinally of the latter 13. The robot 10 is coupled through a turning shaft 15 to the bottom of the second slider 14.
The robot 10 is shown in FIG. 7 in detail. The robot 10 includes a hand 18 which has a pair of finger members 16 on both sides thereof. Both end portions of each of the finger members 16 are formed into fingers 16B and 16C, respectively. The hand 18 is a gear box for changing a turning movement of the turning shaft 15 to an opening and closing movement of the fingers 16B and 16C, shafts 16A provided on both sides of the hand 18 have a function to communicate a motive power from the hand 18 to the fingers 16B and 16C, respectively. Thus the fingers 16B and 16C are movable to and from each other. The fingers 16B are to hold the cassette 2. The fingers 16C are to hold the container 3 or to support the handles 3B from below. The distance between the fingers 16C is larger than that between the fingers 16B. Switching the use of the fingers 16B over to the use of the fingers 16B and vice versa is achieved by turning the hand 18 about the turning shaft 15. In FIG. 5, reference numeral 20 designates a lock/unlock device which drives the lock arms of the bottom lid 4 to connect the latter 14 to the container body 3A or to disconnect the bottom lid 4 from the latter 3A; and 21, a controller for controlling all the internal elements in the stocker 1. Further in FIG. 5, reference character 1E designates a temporary container stand; 1F, a cassette stand; and 1G, shelves on which containers 3 are placed. In the above-described stocker, one robot is provided, and its fingers 16B and 16C are selectively used. On the other hand, a stocker is known in the art in which a robot is provided for handling cassettes, and another robot is provided for handling containers; more specifically, the former robot has fingers for handling cassettes only, and the latter robot has fingers for handling containers only.
In the case of the above-described stocker 1, the cassette 2 containing wafers W is handled as follows: That is, the cassette 2 is carried in the stocker 1, and stored therein, and carried out of the stocker 1 as follows: First, the robot 10 holds an empty container 3 in the container storing chamber 1D, and takes it out of the container storing chamber 1D and places it on the lock/unlock device 20. Under this condition, the lock/unlock device 20 drives the lock arms provided in the bottom lid 4 to disengage the latter 4 from the container body 3A. Next, the robot 10 places the container body 3A on the temporary container stand 1E leaving the bottom lid 4 on the lock/unlock device 20. There-after, the robot 10 switches the fingers 16C over to the fingers 16B; that is, it uses the fingers 16B to move a cassette 2 from the cassette stand 1F, and places it on the bottom lid 4. Next, the robot 10 switches the fingers 16B over to the fingers 16C; that is, the robot 10 uses the fingers 16C to pick up the container body 3A from the temporary container stand 1E and places it on the upper surface of the lock/unlock device 20 in such a manner that the container body 3A covers the cassette 2 from above. In this operation, the bottom lid 4 is engaged with the bottom of the container body 3A. Under this condition, the lock/unlock device 20 drives the lock arms in the bottom lid 4 to secure the latter 4 to the container body 3A. Thus, the cassette has been accommodated in the container 3. Thereafter, the robot 10 moves the container 3 containing the cassette 2 to the container storing chamber 1D, and places it on a predetermined shelf in the container storing chamber. On the other hand, when requested, the robot 10 picks up a container 3 containing a cassette 2 with the fingers 16C, and takes it out of the stocker through the container entrance 1B.
In the above-described conveying system for the stocker, depending on the item (the cassette or the container) to be moved by the robot, two kinds of fingers are selectively used by turning them 180 degrees. Hence, the system suffers from the following difficulties:
(1) The hand and finger members of the robot are unavoidably intricate and bulky, and therefore it is impossible for the robot to make sharp turns; that is, the robot is limited in the range of movement. PA1 (2) The movable weight including the weight of the finger members of the robot is limited. Therefore, if the hand is increased in weight, the movable weight is limited as much. PA1 (3) Since the hand and finger members of the robot are intricate, bulky and heavy, the conveying system including the robot is relatively high in manufacturing cost.